Scanning detection method for environmental gases and laser radar

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0057] As described in the background art, lidar detection can be divided into multiple methods. Among them, differential absorption lidar has realized the detection of multiple gas components in the atmosphere. Differential absorption lidar usually uses two wavelengths of laser light, and one wavelength of laser light The absorption cross-section on the gas to be measured is strong, and the absorption cross-section of the laser with another wavelength on the gas to be measured is weak. By analyzing the ratio of the two laser echo signals, the concentration information of the gas to be measured at different distances can be determined. Differential absorption lidar selects different laser wavelengths according to the specific gas that needs to be detected, so as to realize the detection of different gases, so it has high requirements on the light source.

[0058] Based on this, the embodiments of the present application provide a scanning detection method and lidar for ambient gas, which effectively solves the existing problems in the prior art. The scanning and detection of ambient gas can be achieved only by the wavelength tunable continuous laser, which reduces the lidar The requirements for the light source; and, during the scanning detection process, the frequency of the scanning continuous light is locked, thereby avoiding the detection error caused by the wavelength drift of the wavelength tunable continuous laser light source, and improving the scanning detection accuracy. In order to achieve the above objectives, the technical solutions provided by the embodiments of this application are as follows, specifically combined Figure 1 to Figure 5 The technical solutions provided by the embodiments of the present application are described in detail.

[0059] reference figure 1 As shown, this is a flowchart of a method for scanning and detecting ambient gas provided by an embodiment of the application, wherein the method for scanning and detecting includes:

[0060] S1. Select the first frequency point to the Nth frequency point on the voltage-frequency sweep curve, and the first control voltage to the Nth control voltage corresponding to each frequency point, that is, the ith frequency point corresponds to the ith control voltage, where The voltage-frequency scan curve is the relationship curve between the connected control voltage and the output corresponding frequency within the preset wavelength scan range of the wavelength tunable continuous laser, and the preset wavelength scan range covers the absorption spectrum of the gas to be measured Line, N is an integer not less than 2;

[0061] S2. Control the wavelength tunable continuous laser to output scanning continuous light according to the i-th control voltage, while fine-tuning the i-th control voltage to lock the frequency of the corresponding scanning continuous light at the i-th frequency point, i is not greater than N Positive integer;

[0062] S3. Amplify the scanning pulse light obtained after the scanning continuous light is chopped and emit it to the environment to be measured;

[0063] S4. Collect gas echo signals of the environment to be measured to obtain gas absorption data corresponding to the first frequency point to the Nth frequency point;

[0064] S5. Determine the concentration distribution information of the gas of the type to be measured according to the gas absorption data.

[0065] The embodiment of the present application selects the first frequency point to the Nth frequency point on the voltage-frequency sweep curve, and the first control voltage to the Nth control voltage corresponding to each frequency point. It is understandable that the voltage is controlled by adjusting the piezoelectric ceramic inside the wavelength tunable continuous laser, thereby changing the output frequency of the wavelength tunable continuous laser. If the change of the output frequency with the control voltage is described by a curve, a similar hysteresis loop will appear. Closed curve of line shape. The hysteresis loop shows the relationship between the magnetization M or the magnetic induction intensity B and the magnetic field intensity H during the repeated magnetization of a ferromagnetic substance. When the control voltage changes from small to large, the corresponding output frequency changes from large to small along the higher line; when the control voltage changes from large to small, the corresponding output frequency changes from small to large along the lower line. The starting point control voltage and the voltage values ​​of other points except the end point control voltage correspond to two frequency values. In an embodiment of the present application, the interval between any two adjacent frequency points from the first frequency point to the Nth frequency point provided in the present application is equal.

[0066] reference figure 2 Shown is a graph of a voltage-frequency sweep curve provided by an embodiment of this application, in which the closed curve of the solid line is the voltage-frequency of the control voltage change of the wavelength-tunable continuous laser and its corresponding frequency change. Scanning curve, the closed curve of the solid line represents the control voltage scanning range of the entire wavelength tunable continuous laser, the dotted line represents 2/3 of the entire control voltage scanning range, and the dotted line represents 1/3 of the entire control voltage scanning range.

[0067] It can be seen from the voltage-frequency curve that if the direction in which the control voltage increases is positive, then the positive scan curves corresponding to the positive direction overlap under different control voltage scan ranges; if the direction in which the control voltage decreases is positive, then The scan curves corresponding to the positive direction in different control voltage scan ranges also overlap, so by curve fitting the entire scan curve, multiple points with frequencies corresponding to the control voltage can be obtained on the curve.

[0068] Among them, the embodiments of this application provide figure 2 Taking the increasing direction of the control voltage as a positive example, the open circles represent a series of equally spaced frequency points and their corresponding control voltages taken on the voltage-frequency sweep curve. For this, the actual wavelength tunable continuous laser The control voltage changes and scans according to the taken control voltage.

[0069] Therefore, the voltage-frequency scan curve includes the forward scan line corresponding to the control voltage from small to large and the reverse scan line of the control voltage from large to small; further, in the scanning detection process, the control voltage is first adjusted from small to large. Perform control. After the forward scan line is scanned, the control voltage is controlled from high to low, and then the reverse scan line is scanned. That is, by scanning the frequency of the control voltage in the direction from small to large, after the actual control voltage reaches the selected control voltage from the first control voltage to the Nth control voltage, the frequency lock starts. During the lock process, the control voltage Oscillating back and forth at this position, the voltage value changes very little, which can be regarded as a linear process, and the locking process of a single frequency point can be defined as a scanning step. After the scanning of the entire forward scan line is completed, start to reverse the value of the control voltage, so that the control voltage will return to the initial control voltage position from large to small, and also wait for the actual control voltage to reach the selected first control voltage to the Nth After the control voltage in the control voltage, the frequency lock is started, and then the scanning of the reverse scan line is completed. After the reverse scan line is completed, the corresponding frequency is also the initial frequency value, and then the next detection scanning process is continued.

[0070] Wherein, since the voltage-frequency scanning curve corresponding to the same preset wavelength scanning range is the same, the voltage-frequency scanning curve can be used repeatedly for scanning detection.

[0071] It can be seen from the above content that the technical solution provided by the embodiments of the present application can realize the scanning detection of ambient gas only through the wavelength tunable continuous laser, which reduces the requirements of the laser radar on the light source; and, the scanning continuous light is used in the scanning detection process. The frequency of the tunable continuous laser can be locked to avoid the detection error caused by the wavelength drift of the light source of the wavelength tunable continuous laser, and the scanning detection accuracy can be improved.

[0072] In an embodiment of the present application, the frequency of the scanning continuous light can be locked by monitoring and locking the beat frequency of the wavelength-tunable continuous laser and femtosecond laser. That is, fine-tuning the i-th control voltage to lock the frequency of the scanning continuous light corresponding to the i-th frequency point includes:

[0073] Monitoring the actual beat frequency of the detection continuous light output by the wavelength tunable continuous laser and the femtosecond laser output by the femtosecond laser under the i-th control voltage, wherein the detection continuous light and the scanning continuous light are The split light of the continuous light output by the wavelength tunable continuous laser under the i-th control voltage;

[0074] Using an approximation algorithm, when the difference between the actual beat frequency and the locked beat frequency is greater than the allowable relative deviation value, the i-th control voltage is increased and adjusted, and when the i-th control voltage is increased and adjusted In the process, when the difference between the actual beat frequency and the locked beat frequency is greater than the allowable relative deviation value for a preset number of consecutive times, the adjusted i-th control voltage is reduced until the actual beat frequency The difference between the frequency and the locked beat frequency is within the allowable relative deviation value range. Among them, the preset number of times provided in the embodiment of the present application may be 3 times, so that the frequency locking effect is better.

[0075] It is understandable that in the beat frequency monitoring and locking provided by the embodiments of the present application, a counter can be used to monitor the actual beat frequency of the continuous light detected by the wavelength tunable continuous laser and the femtosecond laser output by the femtosecond laser, and then the counter will The monitoring results are sent to the computer for processing. The computer judges the difference between the actual beat frequency and the locked beat frequency, and then uses an approximation algorithm to fine-tune the control voltage, and finally achieves the purpose of locking the beat frequency, thereby achieving the wavelength The purpose of the frequency locking of the scanning continuous light of the tuned continuous laser; among them, the control of the frequency locking of the scanning continuous light is realized by a counter and a computer, which can effectively avoid the detection error caused by the wavelength drift of the light source of the wavelength tunable continuous laser. Thereby improving the scanning detection accuracy.

[0076] reference image 3 As shown, a schematic diagram of beat frequency locking and corresponding optical frequency changes provided by an embodiment of this application, where: image 3 (a) Represents the process of locking the detection continuous light output by the control voltage controlled wavelength tunable continuous laser with the actual beat frequency of the femtosecond laser output by the femtosecond laser. image 3 Only in figure 2 An example of the first three hollow circles on the middle voltage-frequency sweep curve, step1, step2, and step3 represent 3 beat frequency locking processes respectively, and the middle process of each step is a frequency stepping process; image 3 As shown in (b), the optical frequency of the wavelength tunable continuous laser will be set according to the set step after the beat frequency lock step. figure 2 The value changes corresponding to the open circles on the voltage-frequency sweep curve.

[0077] Further, collecting the gas echo signal of the environment to be measured corresponding to the i-th frequency point provided by the embodiment of the present application includes:

[0078] According to the approximation algorithm, the frequency of the scanning continuous light corresponding to the i-th frequency point is locked, and after the number of consecutive locking reaches 90-110, the gas echo signal of the environment to be measured corresponding to the i-th frequency point is collected.

[0079] It is understandable that this application locks the frequency of the scanning continuous light corresponding to the i-th frequency point according to the approximation algorithm, that is, according to the approximation algorithm, the detection continuous light output by the wavelength tunable continuous laser under the i-th control voltage and the output of the femtosecond laser are detected. The actual beat frequency of the femtosecond laser is locked, and after the number of continuous locking reaches n times, the pulse accumulation starts to collect the gas echo signal of the environment to be measured, where n is 90-110, including the endpoint value. The stability and efficiency of the gas echo signal of the environment to be measured can achieve relatively good results.

[0080] In an embodiment of the present application, collecting the gas echo signal of the environment to be measured provided by the present application includes:

[0081] The gas echo signal of the environment to be measured is collected by means of pulse accumulation.

[0082] Further, the locking process of each frequency point is defined as a scanning step;

[0083] Wherein, from the scanning step corresponding to the center of the absorption spectrum line to the scanning step direction at the two wings of the corresponding absorption spectrum line, the pulse accumulation time corresponding to the scanning step shows a decreasing trend. Among them, the pulse accumulation time of each scan step is different. The pulse accumulation time of the scan step located at the two wings of the absorption spectrum line is shorter than the pulse accumulation time of the scan step at the center of the absorption spectrum line, which realizes non-uniform sampling in the time domain, thereby enabling Improve the signal-to-noise ratio. Among them, the pulse accumulation time of all scanning steps close to the center of the absorption spectrum line is two to three times the pulse accumulation time of all scanning steps located at the two wings of the absorption spectrum line, and the sum close to the center of the absorption spectrum line lies in the absorption line There is no specific restriction on the number of scanning steps on the two wings. If there are 30 scanning steps, the cumulative time of the 15 scanning steps close to the center of the absorption spectrum is 2 to 3 times the cumulative time of the first 7 and the last 8 scanning steps.

[0084] In an embodiment of the present application, the determination of the concentration distribution information of the gas of the type to be measured according to the gas absorption data provided by the present application includes:

[0085] Obtaining gas absorption lines of the gas of the type to be measured at different distances according to the gas absorption data;

[0086] Fitting the gas absorption lines of the type of gas to be measured at different distances;

[0087] Obtain the concentration information of the gas of the type to be measured at different distances from the fitted gas absorption line by searching a database.

[0088] reference Figure 4 As shown, a curve diagram after fitting a gas absorption line of a gas of a type to be measured at any distance provided by this embodiment of the application, Figure 4 The circle in (a) represents the gas absorption line of the gas to be measured at a certain distance, and the solid line represents the result obtained by fitting the gas absorption line of the gas to be measured at a certain distance. , The concentration information of different gases can be obtained by comparing the database. And, by monitoring the beat frequency of the wavelength tunable continuous laser and femtosecond laser, such as Figure 4 As shown in (b), combined with the frequency corresponding to the control voltage on the voltage-frequency scan curve, the frequency of the emitted laser can be determined, thereby fine-tuning the control voltage corresponding to each scan step to suppress the frequency drift of the wavelength tunable continuous laser.

[0089] Optionally, fitting the gas absorption lines of the gas of the type to be measured at different distances provided by the embodiment of the present application is as follows:

[0090] Fitting the gas absorption lines of the gas of the type to be measured at different distances by the galatry function.

[0091] Corresponding to the scanning detection method provided by any one of the above embodiments, an embodiment of the application also provides a scanning detection lidar for ambient gas, wherein the lidar provided by the embodiment of the application includes: a wavelength tunable continuous laser, control processing Module and detection module;

[0092] The control processing module is used to select the first frequency point to the Nth frequency point on the voltage-frequency scan curve, and the first control voltage to the Nth control voltage corresponding to each frequency point, wherein the voltage-frequency scan curve Is the relationship curve between the connected control voltage and the output corresponding frequency within the preset wavelength scanning range of the wavelength tunable continuous laser, and the preset wavelength scanning range covers the absorption spectrum of the gas to be measured, N is An integer not less than 2; and control the wavelength tunable continuous laser to output scanning continuous light according to the i-th control voltage, while fine-tuning the i-th control voltage to lock the frequency of the corresponding scanning continuous light at the i-th frequency point, i is a positive integer not greater than N;

[0093] And, the detection module is used to amplify the scanning pulse light obtained after the scanning continuous light is chopped and emit it to the environment to be measured, and receive the gas echo signal of the environment to be measured; and the control processing module Collect the gas echo signal of the environment to be measured, and obtain the gas absorption data corresponding to the first frequency point to the Nth frequency point according to the gas echo signal of the environment to be measured, and according to the gas absorption data Determine the concentration distribution information of the gas of the type to be measured.

[0094] In an embodiment of the present application, the control processing module provided by the present application fine-tunes the i-th control voltage to lock the frequency of the corresponding scanning continuous light at the i-th frequency point, including:

[0095] Monitoring the actual beat frequency of the detection continuous light output by the wavelength tunable continuous laser and the femtosecond laser output by the femtosecond laser under the i-th control voltage, wherein the detection continuous light and the scanning continuous light are The split light of the continuous light output by the wavelength tunable continuous laser under the i-th control voltage;

[0096] Using an approximation algorithm, when the difference between the actual beat frequency and the locked beat frequency is greater than the allowable relative deviation value, the i-th control voltage is increased and adjusted, and when the i-th control voltage is increased and adjusted In the process, when the difference between the actual beat frequency and the locked beat frequency is greater than the allowable relative deviation value for a preset number of consecutive times, the adjusted i-th control voltage is reduced until the actual beat frequency The difference between the frequency and the locked beat frequency is within the allowable relative deviation value range.

[0097] reference Figure 5 As shown, this is a schematic structural diagram of an ambient gas scanning detection lidar provided by an embodiment of the application, where the control processing module provided by the embodiment of the application includes: a computer 110, a first beam splitter 120, a first Beam combiner 130, balance detector 140, counter 150, detector 160, and capture card 170; and, the detection module includes: chopper 210, first laser amplifier 220, second laser amplifier 230, laser emission system 240 And telescope 250;

[0098] Wherein, the computer 110 is connected to the control terminal of the wavelength tunable continuous laser 300, the output terminal of the wavelength tunable continuous laser 300 is connected to the input terminal of the first beam splitter 120, and the first splitter 120 The first output end of the beamer 120 is connected to the first input end of the first beam combiner 130, and the output end of the femtosecond laser 400 is connected to the second input end of the first beam combiner 130, so The output terminal of the first beam combiner 130 is connected to the input terminal of the balance detector 140, the output terminal of the balance detector 140 is connected to the input terminal of the counter 150, and the output terminal of the counter 150 is connected to the input terminal of the counter 150. The computer 110 is connected;

[0099] And, the second output terminal of the first beam splitter 120 is connected to the input terminal of the chopper 210, and the output terminal of the chopper 210 is connected to the input terminal of the first laser amplifier 220, so The output end of the first laser amplifier 220 is connected to the input end of the second laser amplifier 230, the output end of the second laser amplifier 230 is connected to the input end of the laser emission system 240, and the output of the telescope 250 The terminal is connected with the input terminal of the detector 160, the output terminal of the detector 160 is connected with the input terminal of the collection card 170, and the output terminal of the collection card 170 is connected with the computer 110.

[0100] It is understandable that in the scanning detection lidar of ambient gas provided by the embodiment of this application, the computer selects the first frequency point to the Nth frequency point on the voltage-frequency scanning curve, and the first control voltage to the Nth frequency point corresponding to each frequency point Control the voltage, and then start to control the wavelength tunable continuous laser with the control voltage corresponding to the voltage-frequency sweep curve; the computer is in the process of controlling the wavelength tunable continuous laser with the control voltage from small to large and then from large to small , The detection continuous light output by the tunable continuous laser under the i-th control voltage (obtained by the first beam splitter to split the continuous light output by the tunable continuous laser under the i-th control voltage) and the femtosecond output of the femtosecond laser The laser beams are combined by the first beam combiner, and then transmitted to the balance detector; and the counter monitors the actual detection of the continuous light output by the wavelength tunable continuous laser under the i-th control voltage and the femtosecond laser output by the femtosecond laser Beat frequency, and send the actual beat frequency to the computer; the computer uses an approximation algorithm to increase the i-th control voltage when the difference between the actual beat frequency and the locked beat frequency is greater than the allowable relative deviation value In the process of increasing and adjusting the i-th control voltage, when the difference between the actual beat frequency and the locked beat frequency is greater than the allowable relative deviation value for a predetermined number of consecutive times, the adjusted The i-th control voltage is reduced and adjusted until the difference between the actual beat frequency and the locked beat frequency is within the allowable relative deviation value range.

[0101] At the same time, the chopper chops the scanning continuous light output by the wavelength tunable continuous laser under the i-th control voltage (the first beam splitter splits the continuous light output by the tunable continuous laser under the i-th control voltage). After the wave, the scanning pulse light is output; the scanning pulse light enters the first laser amplifier for pre-amplification, and then enters the second laser amplifier for secondary amplification, and is emitted into the environment to be measured through the laser emission system for detection; and the detector detects through the telescope The gas echo signal of the environment to be measured is transmitted to a collection card for collection; the collection card collects the corresponding from the first frequency point to the Nth frequency point according to the gas echo signal of the environment to be measured The gas absorption data is to send the collected gas absorption data to a computer, and the computer determines the concentration distribution information of the gas of the type to be measured according to the gas absorption data.

[0102] It should be noted that the voltage-frequency sweep curve provided by the embodiment of the present application can be controlled by the computer to control the change in the control voltage of the wavelength tunable continuous laser to control the change in the output frequency of the tuned continuous laser, thereby obtaining the entire preset wavelength scanning range The voltage-frequency sweep curve.

[0103] Further, in order to improve the scanning detection effect of laser, please refer to Figure 5 As shown, the environmental gas scanning detection lidar provided by the embodiment of the present application further includes: an optical modulation unit 510, a second beam splitter 520, a polarization maintaining fiber 530, an attenuator 540, a second beam combiner 550, and a filter Chip 560 and low-pass filter 570;

[0104] The output end of the first laser amplifier 220 is connected to the input end of the optical modulation unit 510, the output end of the optical modulation unit 510 is connected to the input end of the second beam splitter 520, and the second splitter The first output end of the beamer 520 is connected to the input end of the polarization maintaining fiber 530, and the second output end of the second beam splitter 520 is connected to the input end of the attenuator 540. The output end is connected to the first input end of the second beam combiner 550, the output end of the polarization maintaining fiber 530 is connected to the input end of the second laser amplifier 230, and the output end of the telescope 250 is connected to the The input end of the filter 560 is connected, the output end of the filter 560 is connected to the second input end of the second beam combiner 550, and the output end of the second beam combiner 550 is connected to the detector 160 The input terminal is connected, the output terminal of the balance detector 140 is connected to the input terminal of the low-pass filter 570, and the output terminal of the low-pass filter 570 is connected to the input terminal of the counter 150.

[0105] It is understandable that the light modulation unit provided in the embodiment of the present application is used to improve the extinction ratio, where the light modulation unit may be an intensity modulator, an acousto-optic modulator or an optical switch. And, the attenuator is used to compare the reference light (a split light output by the second beam splitter) with the light emitted into the environment to be measured, and then monitor the fluctuation of the reference light through the capture card to return the gas in the environment to be measured. The wave signal is corrected to improve the measurement accuracy; while the polarization-maintaining fiber is used for time delay to facilitate better comparison of the reference light. The optical filter is used to filter out the light that is not within the emission range of the wavelength-tunable continuous laser, so as to facilitate scanning and detection during the day; among them, the polarization-maintaining fiber is a 1km polarization-maintaining fiber. In addition, the low-pass filter facilitates better data processing in order to filter out unnecessary beat frequency signals.

[0106] In an embodiment of the present application, the chopper provided in the present application is a pulse generator, an acousto-optic modulator or a spot light modulator. And, the detector is a superconducting detector. And, the laser emitting system and the telescope provided in the embodiment of the present application are in a separate transceiver structure;

[0107] Alternatively, the laser emitting system and the telescope are coaxial transmission and reception structures

[0108] Further, in order to optimize the light output of the wavelength tunable continuous laser, the embodiment of the present application may perform calibration processing on the preset wavelength scanning range. That is, the preset wavelength scanning range is a wavelength scanning range calibrated according to the gas of the type to be measured.

[0109] For the calibration structure, refer to Figure 5 As shown, the environmental gas scanning detection lidar provided by the embodiment of the present application further includes: a third beam splitter 610, an ASE light source 620, a gas cavity 630, a third beam combiner 640, and a spectrometer 650;

[0110] The second output terminal of the first beam splitter 120 is connected to the input terminal of the third beam splitter 610, and the first output terminal of the third beam splitter 610 is connected to the input terminal of the chopper 210 Connected, the second output end of the third beam splitter 610 is connected to the first input end of the third beam combiner 640, and the output end of the ASE light source 620 is connected to the input end of the gas cavity 630, The gas chamber 630 stores the gas of the type to be measured, the output end of the gas chamber 630 is connected to the second input end of the third beam combiner 640, and the output end of the third beam combiner 640 Connect with the input end of the spectrometer 650.

[0111] It is understandable that the light emitted from the ASE light source provided in the embodiment of the present application passes through the gas cavity, and then the light output from the gas cavity displays the absorption spectrum of the gas to be measured through the spectrometer; at the same time, the wavelength tunable continuous laser is emitted Part of the light (the light split by the first beam splitter and the third beam splitter) is connected to the spectrometer, and then the wavelength of the wavelength tunable continuous laser is adjusted to be within the preset wavelength scanning range covering the absorption line Variety.

[0112] The embodiment of the application provides a scanning detection method and lidar for ambient gas, including: selecting a first frequency point to an Nth frequency point on a voltage-frequency scanning curve, and the first control voltage to the first control voltage to the first frequency point corresponding to each frequency point N control voltage, wherein the voltage-frequency scan curve is the relationship curve between the connected control voltage and the output corresponding frequency within the preset wavelength scan range of the wavelength tunable continuous laser, and the preset wavelength scan range covers the The absorption spectrum of the gas of the test type, N is an integer not less than 2; the wavelength tunable continuous laser is controlled according to the i-th control voltage to output scanning continuous light, and the i-th control voltage is fine-tuned to adjust the i-th frequency Point corresponding to the frequency of the scanning continuous light to lock, i is a positive integer not greater than N; the scanning pulsed light obtained after the scanning continuous light is chopped is amplified and then emitted to the environment to be measured; gas in the environment to be measured is collected Echo signals to obtain gas absorption data corresponding to the first frequency point to the Nth frequency point; and determine the concentration distribution information of the gas of the type to be measured according to the gas absorption data.

[0113] It can be seen from the above content that the technical solution provided by the embodiments of the present application can realize the scanning detection of ambient gas only through the wavelength tunable continuous laser, which reduces the requirements of the laser radar on the light source; and, the scanning continuous light is used in the scanning detection process. The frequency of the tunable continuous laser can be locked to avoid the detection error caused by the wavelength drift of the light source of the wavelength tunable continuous laser, and the scanning detection accuracy can be improved.

[0114] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in this document can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown in this text, but should conform to the widest scope consistent with the principles and novel features disclosed in this text.